Abstract Consumption of sugar-sweetened beverages (SSB) is a risk factor for obesity, diabetes, and other chronic diseases. Latinos are among the groups with the highest prevalence of diabetes and SSB consumption in the US. Consumption of SSB begins at an early age and may have cumulative detrimental consequences to health later in life. There is an urgent need to facilitate reduction of SSB consumption among young Latino children before this behavior becomes part of an unhealthy lifestyle. The public health recommendation to drink water instead of SSB does not consider the multiple barriers that underserved communities face when choosing a beverage in an environment with limited access to clean, palatable drinking water, and saturated with SSB promotion. Using a community participatory approach, we developed an intervention, Water Up! at Home, which draws on theory and community experience to position parents as social models for their young children. The objective of the current proposal is to test the preliminary effects of this intervention to replace SSB with filtered tap water among low-income Latino parents and their children (6 months-3 year olds). Our working hypothesis is that by addressing sociocultural (via curriculum) and physical (via water filter) barriers, parents can reduce their own and their children's SSB consumption. We will use a multiphase sequential mixed-methods design to integrate qualitative and quantitative findings. Aim 1) Partnering with an existing home visting program of Early Head Start, we deliver the intervention to replace SSB with filtered tap water at home and test its effects using a randomized control trial. H1) Parents randomly assigned to the Water Up! at Home program (n=38) will see a net reduction of 0.5 servings/day of SSB compared with the control group at the end of the intervention (12 weeks). H2) We will see a similar reduction in SSB consumption among young children. Exploratory aim: 12 months after baseline, we will explore changes on body mass index and waist circumference of parents. To assess the quality of program implementation, we will use a summative process evaluation. Aim 2) To assess the psychosocial mediators of intervention effects and to understand why the program was or was not successful, we will conduct 30 in-depth interviews with parents, segmented by whether they responded positively/negatively to the intervention. We will also conduct two focus groups with Early Head Start staff (n=10) to describe the aspects of the intervention design, context, implementation and delivery that may affect program impact, its sustainability and practicability. The study addresses a novel paradigm that posits water security at home as a determinant of SSB consumption among low-income Latino parents and their children. This study advances NIDDK's mission by addressing diabetes risk factors in a hard-to-reach, high-risk population via the relatively under-used home-visiting programs. In response to the FOA, this study also allows a new investigator (from an underrepresented background in behavioral sciences) to collect preliminary data to design a robust R01 independent proposal.